A contrast of networking technologies.

1. SONET,
CWDM, DWDM
RISHABH DUBEY (N015)

2. TELEPHONE NETWORKS {BRIEF
HISTORY}
• Digital carrier systems
• The hierarchy of digital signals that the telephone
network uses.
• Trunks and access links organized in DS (digital
signal) hierarchy
• Problem: rates are not multiples of each other.
• In the 1980’s Bellcore developed the
Synchronous Optical Network (SONET)
standard.
• Previous efforts include: ISDN and BISDN.

3. SONET
• Transmission links of the telephone network
have been changing to SONET where rates are
arranged in STS (Synchronous Transfer Signal)
hierarchy.
• The hierarchy is called SDH (Synchronous
Digital Hierarchy) defined by CCITT.
• It is an ITU standard.

4. SONET
SONET:: encodes bit streams into optical signals
propagated over optical fiber. SONET defines a
technology for carrying many signals of different
capacities through a synchronous, flexible, optical
hierarchy.
• A bit-way implementation providing end-to-end
transport of bit streams.
• All clocks in the network are locked to a common master
clock so that simple TDM can be used.
• Multiplexing done by byte interleaving.
• SONET is backward compatible to DS-1 and E-1 and
forward compatible to ATM cells.
• Demultiplexing is easy.

5. COMPARISON BETWEEN
CWDM & DWDM
TECHNOLOGY

6. For a better signal transmission in fiber-optic communication, different kinds
of technologies are applied to the industry. Wavelength-division multiplexing
(WDM) is one of the commonly used technologies which multiplexes a
number of optical carrier signals onto a single optic fiber by using different
wavelengths of laser light. That is to say, WDM enables two or more than
two wavelength signals to transmit through different optical channels in the
same optical fiber at the same time.

7. • There are two types of divisions WDM system-
• CWDM (coarse wavelength division multiplexing)
• DWDM (dense wavelength division multiplexing).
• They are both using multiple wavelengths of laser light for signal transmission on a
single fiber. However, from the below aspects
• Channel spacing,
• Transmission reach,
• Modulation laser
• Cost,
• CWDM and DWDM still have a lot of differences. This document will focus on these
distinctions and hope you can have a general understanding about CWDM and
DWDM technology.

8. CHANNEL
SPACING
• As their names suggest, the words “coarse” and “dense” reveal the
difference in channel spacing. CWDM has a wider spacing than DWDM. It
is able to transport up to 16 wavelengths with a channel spacing of 20 nm
in the spectrum grid from 1270 nm to 1610 nm. But DWDM can carry 40,
80 or up to 160 wavelengths with a narrower spacing of 0.8 nm, 0.4 nm or
0.2 nm from the wavelengths of 1525 nm to 1565 nm (C band) or 1570 nm
to 1610 nm (L band). It is no doubt that DWDM has a higher performance
for transmitting a greater number of multiple wavelengths on a single
fiber.

10. TRANSMISSION
REACH
• Since the wavelengths are highly integrated in the fiber during light
transmission, DWDM is able to reach a longer distance than CWDM. The
amplified wavelengths provide DWDM with the ability of suffering less
interference over long-haul cables. Unlike DWDM system, CWDM is
unable to travel unlimited distance. The maximum reach of CWDM is
about 160 kilometers but an amplified DWDM system can go much further
as the signal strength is boosted periodically throughout the run.

11. MODULATION
LASER
• CWDM system uses the uncooled laser while DWDM system uses the
cooling laser. Laser cooling refers to a number of techniques in which
atomic and molecular samples are cooled down to near absolute zero
through the interaction with one or more laser fields. Cooling laser adopts
temperature tuning which ensures better performance, higher safety and
longer life span of DWDM system. But it also consumes more power than
the electronic tuning uncooled laser used by CWDM system.

12. COST
• Because the range of temperature distribution is nonuniform in a very wide
wavelength, so the temperature tuning is very difficult to realize, thus using
the cooling laser technique increases the cost of DWDM system. Typically,
DWDM equipment is four or five times more expensive than CWDM
equipment.

13. CONCLUSION
• CWDM and DWDM are both coming from the WDM technology that is
capable of conveying multiple wavelengths in a single fiber. But with
different characteristics, people should think twice before choosing the
CWDM or DWDM system. CWDM usually costs less but its performance
is far behind DWDM. Both your requirements and budget need to be taken
into consideration. Moreover, the WDM products including CWDM
mux/demux module, DWDM mux/demux module and optical splitter are
highly welcome in the market.